Polyunsaturated fatty acids of the n-3 or n-6 type are not synthesized de novo in animal tissue. Although polyunsaturated fatty acids can be synthesized by the elongation and desaturation enzymes of animal tissue, the n-3 or n-6 type of structures can only be obtained from dietary sources. The presence and amounts of the n-3 or n-6 type polyunsaturated fatty acids in animal tissue reflects the origin of these two types of fatty acids in plant tissues used as sources of food. The essential polyunsaturated fatty acids usually found in plant tissue include linoleic acid (18:2n-6) and α-linolenic acid (18:3n-3). When an animal is fed with a source of n-3 or n-6 polyunsaturated fatty acids, displacement of endogenous fatty acids (20:3n9 and 20:4n-7 types) occurs, resulting in the enrichment of n-3 and n-6 highly unsaturated fatty acids (HUFA), specifically 20:4n-6, 20:5n-3, 22:5n-3, 22:6n-3. Because the precursors of the n-3 and n-6 HUFAs can only be obtained from dietary sources, their relative abundance in tissues is limited by the availability of these precursors in the diet.
The 20-carbon HUFAs play important roles as substrates and antagonists of eicosanoid biosynthesis. Altering the abundance of dietary precursors of these HUFAs may influence a tissue's capacity to form specific eicosanoids. An altered capacity in turn may affect the frequency and severity of eicosanoid-related disorders, such as cardiovascular disease and osteo and rheumatoid arthritis. It is also known that optimizing the enrichment of these HUFAs can be used to treat or affect a variety of conditions, including but not limited to, inflammatory, developmental, renal, dermatological, and blood pressure related conditions.
Thus, it would be desirable to have a method to predict the enrichment of n-3 and n-6 type HUFAs in plasma and cells of canines based on the amount of polyunsaturated fatty acids (PUFA) in the diets. It would further be desirable if the method could determine the enrichment of n-6 and n-3 type PUFAs in the triglycerides (TG) or HUFAs in the phospholipids (PL) formed in plasma or neutrophils. Formulae have been developed for predicting n-3 and n-6 type HUFA in Humans, Lands, W. E. M. et al., Biochem. Biophys. Acta, 1180, 147-162 (1992), and in rats, Lands, W. E. M. et al., Lipids, 25, 505-516 (1990). However, no such formulae have been previously available for predicting n-3 and n-6 type HUFA in canines. Without such equations, effectiveness of a proposed diet formulation would be tested by feeding the proposed diet to a group of dogs for a period of time, perhaps 3-4 weeks or more, and subsequently measuring the plasma and neutrophil levels of fatty acids and levels of enrichment. If the measurements indicated that adjustments to the proposed diet were necessary, the adjusted proposed diet similarly may be fed to a group of dogs, to determine if the proper levels were reached. Thus, it could take weeks or months to determine if the desired fatty acid levels would be reached using a proposed diet formulation.